This invention relates to the scanner for optically scanning a subject such as an electro-optic scanner of a photographic film for imprinting image data on the film and, more particularly, to the use of an optical diffraction grating disposed on a holder of the film for increased accuracy in positioning an optical beam upon the film.
One form of electro-optic scanner employs a scanning mirror which directs a beam of light to a subject, such as a photographic film, and scans the beam across the film by a pivoting motion of the mirror. Accurate scanning of the subject requires knowledge of the beam location on the subject during all parts of the beam scan.
The typical scanner may be employed for reading an image of the subject, such as a photographic image, and for storing data in a digital memory at locations corresponding to the beam positions. Alternatively, the scanner may be employed in a writing mode for writing pixels of image data from locations within a memory to corresponding locations on a photographic film. In both cases, knowledge of beam location may be obtained from the mirror pivot angle or from an electric current which drives a motor, such as a galvanometer, to pivot the mirror.
A problem arises in that there may be an error in determination of beam location based on a knowledge of the motor current due to the dynamic behavior of the mirror. For example, the beam may be one or more pixels ahead or behind of a presumed beam location, particularly in a scanning system employing very high resolution. As a result, errors and/or image degradation may occur during either a reading or a writing of image data.